Structure for transmitter bandwidth optimization circuit

ABSTRACT

A design structure embodied in a machine-readable medium used in a design process provides a transmitter having a frequency response controllable in accordance with an operational parameter, and may include a storage operable to store operational parameters for controlling a frequency response of the transmitter under each of a plurality of corresponding operating conditions. A sensor can be used to detect an operating condition. In response to a change in the detected operating condition, a stored operational parameter corresponding to the detected operating condition can be used to control the frequency response of the transmitter.

BACKGROUND OF THE INVENTION

The present invention relates to microelectronic transmitters,particularly to their structure and operation.

High-speed microelectronic serial data transmitters can transmit atrates of multiple gigabits per second (Gbs) and even tens of Gbs. Suchhigh-speed serial transmitters typically are implemented onmicroelectronic elements, e.g., semiconductor chips, with severaltransmitters implemented on each microelectronic element.

The bandwidth of a transmitter refers to a range of frequencies forwhich the output of the transmitter has about the same amplitude.Ideally, the bandwidth of a serial data transmitter should stay constantthroughout the range of operating conditions that the transmitterencounters. Maintaining bandwidth helps to reduce energy consumption andcan reduce cross-talk noise between adjacent transmitters on the samemicroelectronic element.

Sometimes, a transmitter design is required to accommodate differentcustomer specifications with a wide range of data rates. Aone-design-fits-all practice has become a norm for the semiconductorindustry to save design cost. However, transmitters designed this waycan sometimes have difficulty meeting the bandwidth requirements fortransmission at the highest data transmission rates.

FIG. 1 contains Bode plots (curves) illustrating an amplitude versusfrequency response of a prior art serial transmitter under differentoperating conditions. Curve 10 is a graph illustrating nearly idealamplitude versus frequency response for the transmitter. In this case,the amplitude is fairly constant at amplitude a0 in the frequency rangef0 to f_(max). The frequency response exhibited by curve 10 will resultunder a fairly narrow range of operating conditions, such as when thetemperature of the microelectronic element and the voltage level of thepower supply voltage supplied to the transmitter are close to ideal.Unfortunately, operating conditions, including temperature and powersupply voltage level are frequently at levels which are not close toideal. The temperature may vary between subzero temperatures uponpowering up the transmitter in cold locations to over 100 degrees C. insome densely packed environments. The power supply voltage level mayalso vary, for example, between 1.0 V and 2.5 V (by as much as 150%).Curve 12 illustrates a frequency response of the transmitter underdifferent, non-ideal operating conditions, for example, when temperatureis elevated and the power supply voltage level is decreased. Asillustrated by curve 12, the frequency response under the non-idealoperating conditions worsens. The amplitude rolls off (decreases) at alower frequency (f_(R)) than f_(max), such that bandwidth under thenon-ideal operating conditions is impacted. At frequency f_(max) of thecurve 12, the amplitude has already fallen from the initial amplitude a1to a decreased amplitude a2, for a total decrease in amplitude of Δa. Itis difficult, if not impossible, to design a serial data transmitterwhich has satisfactory frequency response under the different extremesof operating conditions.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a design structure,embodied in a machine-readable medium used in a design process. Thedesign structure can include a transmitter having a frequency responsecontrollable in accordance with an operational parameter. The designstructure may include storage, which can include, for example,non-volatile memory, or a plurality of fusible links. The storage may beusable to store operational parameters for controlling a frequencyresponse of the transmitter under each of a plurality of correspondingoperating conditions. The design structure may also include a sensoroperable to detect at least one operating condition. A plurality ofsensors may be provided, for example, for detecting temperatures andpower supply voltages at locations on the microelectronic element. Thedesign structure may further include a control circuit which is operablein response to a change in a detected operating condition to use astored operational parameter corresponding to the detected operatingcondition to control the frequency response of the transmitter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a Bode plot graph illustrating differences in frequencyresponses for a prior art transmitter.

FIG. 2A is a block and schematic diagram illustrating a microelectronictransmitter in accordance with an embodiment of the invention.

FIG. 2B is a table illustrating a set of stored operational parametersfor each of an n×m matrix of operating conditions.

FIG. 3 is a schematic diagram illustrating a programmable peakingamplifier.

FIG. 4 is a flowchart illustrating a method of operation in accordancewith an embodiment of the invention.

FIG. 5 is a schematic diagram illustrating operation of amicroelectronic transmitter during a calibration method of operation inaccordance with an embodiment of the invention.

FIG. 6 is a flowchart illustrating a calibration method of operation inaccordance with an embodiment of the invention.

FIG. 7 is a flowchart illustrating a calibration method of operation inaccordance with a particular embodiment of the invention.

FIG. 8 is a Bode plot graph further illustrating a calibration method ofoperation in accordance with an embodiment of the invention.

FIG. 9 is a block diagram of an exemplary design flow such as can beused in fabrication of a design structure in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

Commonly owned U.S. patent application Ser. No. 11/769,128 filed Jun.17, 2007 to Louis L. Hsu et al. entitled “Transmitter BandwidthOptimization Circuit” is incorporated by reference herein. In general,in today's manufacturing environment, from lot to lot or even from chipto chip, an acceptable process tolerance is assumed. The resulting chipmay experience a distribution in process parameters (also called “P”factor) such as gate dimensions, gate dielectric thickness, thresholdlevels, line widths, distance to shallow trench isolation, overlay,misalignment, etc. As the devices approaching 65 nanometers (nm) andbeyond, the leakage through the gate dielectric will aggravate theprocess variation. A precision analog circuit must be able to calibrateout such P-related variation so that DC offset due to device mismatchcan be eliminated. The on-chip power supply voltage can also vary (alsocalled “V” factor). Even if the power supply voltage level set at aknown level, it could also vary due to aging, resistive (“IR”) drop,leakage or power disruption. A calibration method is needed which cancompensate for P related variations Finally, circuit behavior isinfluenced by on-chip temperature variation, as mentioned earlier,called T-factor. In accordance with an embodiment of the invention, aprecision transmitter can be achieved which is tolerant to real-life PVTvariation.

FIG. 2A illustrates a microelectronic element 200 including atransmitter 202 in accordance with an embodiment of the invention. Thetransmitter 202 typically is a serial data transmitter which outputs adata signal as a pair of differential signals Dn and Dp on a pair oftransmission lines terminated by termination impedances Zn and Zp. Themicroelectronic element 200 includes a system operable to control thefrequency response of the transmitter 202. Illustratively, as shown inFIG. 2A, such system includes sensors 205 which are operatively coupledto logic circuits 210, the logic circuits further being coupled toparameter storage 220, which in turn, is coupled to the transmitter 202.The parameter storage 220 is operable to store a plurality ofoperational parameters for controlling a frequency response of thetransmitter under various operating conditions. Temperature and powersupply voltage level are among the operating conditions which can varyduring operation of the microelectronic element. The length of a cableto which the transmitter 202 is connected is another operating conditionwhich can vary and affect the frequency response of the transmitter. Thedata transmission rate at which the transmitter is operated can beanother operating condition for which control over the frequencyresponse is desired. For example, in a case where the transmitter isoperated at a lower data transmission rate, the frequency response mayimprove if amplitude is increased at a lower frequency, but allowed toroll off at a decreased maximum frequency. Another operating conditionthat can vary and affect frequency response relates to whether thetransmitter is coupled to the receiver in an AC-coupled manner or aDC-coupled manner. The distance between adjacent transmitters on themicroelectronic element is yet another variable which, like otheroperating conditions, can affect the frequency response and for whichcorresponding operational parameters can be stored.

In accordance with an embodiment of the invention, the system isoperable to retrieve and use the operational parameters stored in thestorage 220 to control operation of the transmitter to obtain goodfrequency response and bandwidth at a plurality of different operatingconditions. Using the stored parameters, the frequency response of thetransmitter 202 is controlled so that it more closely resembles thecurve 10 (FIG. 1; ideal frequency response), despite changes in theoperating conditions such as temperature, power supply voltage level orcable length. Moreover, operational parameters can be stored which canbe used to compensate for design-level changes such as the spacingbetween adjacent transmitters.

FIG. 2B is a chart illustrating an n×m matrix (the numbers n and m maybe different) of operational parameters for controlling the transmitterunder different temperature and power supply voltage operatingconditions. For each supply voltage value of a set of supply voltagevalues and each temperature value of a set of temperature values, thereis an operational parameter for use in controlling the operation of thetransmitter. In one example, the supply voltage provided to thetransmitter can vary between 1.0 V and 2.5 V. The temperature of themicroelectronic element can vary between 0 and 100 degrees C. The n×mmatrix provides operational parameters for controlling the frequencyresponse of the transmitter under each of the different operatingconditions defined by the combination of the supply voltage level andthe temperature. Within the matrix, operational parameters can bestored, for example, for temperature gradations of 10° C. and gradationsin the power supply voltage of 100 mV.

Therefore, when the supply voltage has a first value, e.g., 1.0 V, andthe temperature of the microelectronic element has a value oftemperature #2, e.g., 10° C., then, the matrix contains an operationalparameter 250 for controlling the transmitter under those operatingconditions to obtain good frequency response. When the supply voltage isone gradation higher but the temperature is the same, a differentoperational parameter 252 is used to control the operation of thetransmitter. Alternatively, when the temperature is one gradation higherbut the supply voltage is the same, another operational parameter 254 isused to control the operation of the transmitter.

In operation, sensors 205 detect values of operating conditions whichaffect the microelectronic element, for example, a temperature of themicroelectronic element and a level of the power supply voltage suppliedto the microelectronic element. The detected values are provided tologic circuit 210 which then determines whether the operating conditionshave changed since the time of last reading. If the logic circuits 210detect no change in the operating conditions, the transmitter 202continues to operate with previously applied operational parameterscontrolling its frequency response. However, when the logic circuits 210detect a change, corresponding operational parameters are retrieved fromstorage 220 and applied to control the operation of the transmitter 202.

The transmitter 202 requires circuitry which has a controllablefrequency response. A programmable peaking amplifier 300 (FIG. 3) is anexample of such circuit. The peaking amplifier 300 can be controlled asan in-line amplifier in the differential data transmitter 202 (FIG. 2A)to obtain desired frequency response over the operating bandwidth of thetransmitter. A “peaked” frequency response exhibits increased amplitudeat a particular frequency. Curves 883 and 884 (FIG. 8), discussed below,exhibit peaked frequency response. Peaked frequency response iscontrasted with non-peaked frequency response, as exemplified by curve881 (FIG. 8). The programmable peaking amplifier 300 includes elementswhich cause its frequency response to be more like the non-peakedfrequency response at lower frequencies and to be more like the peakedfrequency response curve when close to the highest output frequencyf_(max). In such way, the frequency response appears similar to theideal frequency response curve 10 shown in FIG. 1.

To achieve such frequency response, the peaking amplifier 300 includesboth non-peaking load elements and peaking load elements. Non-peakingload elements include resistive loads RN and RP operable to generateoutput signals OUTP and OUTN, respectively. Each of the output signalsOUTP and OUTN swings by a resistive voltage drop from the supply voltage302 in response to input signals INN and INP applied to inputtransistors T1 and T2. Peaking load elements include shunt resistors R1,R2 and R3 and shunt capacitors C1, C2 and C3. The shunt resistors andshunt capacitors have different resistance values and capacitancevalues. The shunt resistors and shunt capacitors can be switched intothe peaking amplifier circuit and switched out by a set of digitalcontrol signals s1, s2, s3, s4, s5 and s6 applied to pairs of switchingdevices, e.g., a pair of devices n1 . . . to the pair of devices n6. Inthis way, the peaked frequency response of the peaking amplifier can bevaried in accordance with the control signals s1, s2, s3, s4, s5 and s6.

The operational parameters stored in the parameter storage 220 (FIG. 2A)are used to control the values of the digital control signals s1, s2,s3, s4, s5 and s6 applied to the peaking amplifier 300. The values ofthe control signals s1, s2, s3, s4, s5 and s6 for operating thetransmitter at a given set of operating conditions can be storeddirectly in a decoded form as a set of one-bit values making up theoperational parameters. Alternatively, the control signals can be storedin another form, e.g., an encoded form, and then converted to decodedsignals s1, s2, s3, s4, s5 and s6 for application to the switchingdevices of the peaking amplifier 300.

FIG. 4 is a flowchart illustrating an exemplary method for operating thetransmitter and controlling its frequency response. In normal operation(block 410) of the transmitter, sensors, e.g., 205 (FIG. 2A) are used todetect an operating temperature and a level of a power supply voltageapplied to the transmitter (block 420). From the detected temperatureand voltage, a “code” is determined, as from a look-up table. From thecode, in block 430 a set of operational parameters, e.g., values ofcontrol signals, such as signals s1, s2, s3, s4, s5, and s6 areretrieved from the parameter storage 220 (FIG. 2A). The peakingamplifier 300 (FIG. 3) of the transmitter is updated in accordance withthe operational parameters. The transmitter now operates in accordancewith the updated parameters. Subsequently (block 440), the temperatureand voltage level are detected again using sensors 205 and the codecorresponding to the detected values is obtained from the look-up table.The currently obtained code is then compared with the most recently usedcode. If the code has not changed, operation continues by monitoringtemperature and voltage again from step 440. However, when the code haschanged, operation continues at step 430 in which the new code is usedto retrieve anew a set of operational parameters from the parameterstorage 220 (FIG. 2A). The transmitter 202 then is operated inaccordance with the newly retrieved set of parameters. Thereafter,operation continues by monitoring again the temperature and voltage(step 440).

The foregoing discussion assumes that operational parameters are alreadystored in the parameter storage 220 (FIG. 2A). The remaining descriptionrelates to ways of determining the operational parameters that are to bestored in the parameter storage 220.

In one embodiment, the operational parameters are determined withrespect to samples of microelectronic elements in calibration tests at aproduction or test facility. Test conditions applied to the samplemicroelectronic elements are varied between minimum and maximum valuesfor a matrix of n operating conditions. Samples having different designconditions such as different spacings between adjacent transmitters canbe tested to determine matrices of n operating conditions for suchsamples, as well. Operational parameters for each set of operatingconditions or design conditions can then be determined by applyinginitial operational parameters, testing the frequency response, changingthe operational parameters if needed, and recording final operationalparameters when the frequency response is satisfactory. The recordedfinal operational parameters are then provided as a set of data to beloaded into non-volatile memory, e.g., flash memory of the generalpopulation of chips which will be incorporated and used in aninformation handling system (e.g., processing or communication) systemfor use. Alternatively, the operational parameters can be stored byburning fusible links, e.g., fuses, antifuses, etc., on the generalpopulation of chips using electrical or laser equipment.

In another embodiment, the above-described calibration tests can beperformed by built-in test algorithms which operate on each chipindividually as installed in an information handling system for use.Here, it is possible that the calibration tests will cover a smaller setof operating conditions than the calibration tests done on samples asdescribed above. For example, it may not be possible for the temperatureor the power supply voltage level to vary by more than a small amountafter the chip is installed in the information handling system. However,the range of variation of the operating conditions during calibrationtesting suffices because in operation, the range of variation is notexceeded.

In a particular embodiment, the bandwidth of the serial data transmitteris calibrated during a power-on-sequence for a plurality of differentoperating conditions. During the power-on-sequence, the transmitter isoperated under a plurality of different operating conditions includingdifferent temperatures and power supply voltage levels. Settings appliedto the peaking amplifier are adjusted for each set of operatingconditions until the required frequency response is attained. Thesettings of the peaking amplifier are then stored as operationalparameters for operating the transmitter.

FIG. 5 is a schematic diagram illustrating a system included within amicroelectronic element 500 which is operable to calibrate a transmitter520 under a plurality of different operating conditions. The system isused to record a set of operational parameters in storage 531 forcontrolling the transmitter's frequency response. The system can beutilized during a non-transmitting interval such as during or followinga power-on-reset of the transmitter 520. The system includes transmittercontrol logic 510 operable to output a test data pattern fortransmission by the transmitter 520. The control logic can output thetest pattern at different transmission rates. The transmitter outputs aserial differential data signals Dn and Dp onto a pair of signal lines514, 512, each of which is terminated by respective impedance matchingnetworks 511, 513, for example, 50 ohm terminations.

Sensors 533 include a sensor which detects an operating temperature, asensor which detects a power supply voltage level and sensors whichdetect an amplitude level of the differential data signals Dn and Dppresent on the signal lines 514, 512. The output of the sensors 533 aresupplied to logic circuits 532, which, in turn, are connected toparameter storage 531. As in the above example, FIG. 2A, the parameterstorage 531 is coupled to the transmitter 520 to provide parameters forcontrolling its frequency response.

FIG. 6 is a flowchart illustrating a method of calibrating atransmitter, e.g., transmitter 520 (FIG. 5), in accordance with anembodiment of the invention. When calibration begins (610), a set ofoperational parameters are retrieved (620) from storage and used tocontrol the transmitter's frequency response. The transmitter is set toan initial condition for transmitting a data pattern at a particulardata transmission rate. The transmitter also begins at a beginningtemperature and beginning power supply voltage level. These conditionsmay be forced by circuitry on the chip or external circuitry.Alternatively, the different temperature and voltage conditions mayoccur as a result of the length of time the chip is operating since thechip was last powered on, with faster rises occurring in temperaturewhen the chip has been recently powered on.

In one example, the retrieved parameters can be used to apply controlsignals s1, s2, s3, s4, s5, s6, etc., to a peaking amplifier 300 asillustrated in FIG. 3. The frequency response of the transmitter intransmitting the data pattern at the particular data transmission rateis then checked (630). If satisfactory, the operational parameters thenare stored (640) as the valid parameters for use in controllingtransmitter at the particular temperature, voltage and data transmissionrate conditions. In block 650, it is checked to determine whether thecalibration test has reached the last temperature and voltage conditionsto be tested. If so, then the calibration test ends (680).

However, many different temperature and voltage conditions are to betested. Step 660 represents a change in temperature and voltageconditions applied to the microelectronic element, which can occur byforcing, or by waiting for conditions, e.g., temperature, to changenaturally, or by a combination of the same. Therefore, 670 represents astep of achieving the next temperature and power supply voltagecondition, which may involve waiting, feedback control, or both toachieve. Once the next set of temperature and voltage conditions isachieved, the frequency response of the transmitter is checked again(630) and the above-described process of updating transmitter parametersand checking the frequency response is repeated until satisfactoryfrequency response is obtained under those temperature and voltageconditions. Then, the process repeats again for the next set oftemperature and voltage conditions until the last set of conditions hasbeen tested, at which time the calibration is complete (680).

FIG. 7 is a flowchart illustrating a particular method of calibration inaccordance with an embodiment of the invention. The flowchart is readfrom right to left. Calibration testing begins by testing transmitteroutput signal amplitude using an initially low data transmission rateand known temperature and voltage conditions (700). In block 701, theoutput signals of the transmitter are sampled at the designated datarate. In block 702, the amplitude of each signal then is compared to apreset target amplitude, and in block 703, a decision is made whetherthe signal amplitude is greater than the preset target amplitude.

The performance of the method illustrated in FIG. 7 is best understoodwith reference to illustrative Bode plots of transmitter output signals(FIG. 8). As shown in FIG. 8, curve 881 represents a frequency responseof the transmitter with no peaking or very little peaking applied. Curve882 represents a desirable frequency response which is almost flatthroughout the entire passband and does not show much decrease untilabove frequency f3, which can be considered the roll-off frequency.Curves 883 and 884 illustrate the signal amplitude under conditions ofincreased peaking. The increased peaking causes the signal amplitude atlower frequencies to fall well below the nominal amplitude a0, makingthese conditions undesirable for transmitting.

During this initial calibration test, the data rate is set to a low datatransmission rate f1 (FIG. 8), such as a rate which is ⅕ of the normalpeak data transmission rate f_(max). Therefore, when the decision atblock 703 is no, the signal amplitude at the lower frequency f1 isaffected. Low signal amplitude at frequency f1 indicates that too muchpeaking is being applied to the transmitter. Therefore, under suchcondition, the amount of the applied peaking then is reduced (704). Theamount of peaking then is reduced by reducing the value of the shuntcapacitance (from among C1, C2 and C3; FIG. 3) connected between thelegs of the peaking amplifier 300. Operation then continues again fromstep 701.

On the other hand, when the signal amplitude is greater than the presettarget, operation then continues by increasing the data transmissionrate (710) to the peak transmission rate f_(max) (FIG. 8). With the newtransmission rate, output signals are now sampled at the f_(max) rate(711). The signal amplitude is compared to a preset target (712). If thesignal amplitude is lower than the preset target, in this case,insufficient peaking is applied to the transmitter. Insufficient peakingis exemplified by curve 881 which begins rolling off before reachingf_(max) and has lower signal amplitude at f_(max). Therefore, when thesignal amplitude is lower than the preset target, the amount of peakingis increased (714) and operation then continues at step 711.

Otherwise, when the signal amplitude is greater than the preset target,operation then continues by increasing the data transmission rate (720)to the f3 frequency (FIG. 8), a frequency which represents a designedpassband limit of the transmitter in order for the transmitter totransmit at the peak rate of f_(max). F3 is sometimes referred to as a“3 dB frequency”, but it is not intended to require that signalamplitude at that frequency is reduced by 3 dB. Similar to theoperations described above, the output signals are then sampled (721) atf3 rate, after which the signal amplitude is compared to a preset target(722). Then, when signal amplitude is greater than the preset target, itis presumed that the amount of peaking is too much, since the signalamplitude will more closely reflect curves 883 and 884 than curves 881,882 (FIG. 8). Therefore, in such case, a decision is made to reduce thepeaking (721) and then operation continues from step 721. Alternatively,when the signal amplitude is not greater than the preset target, thenthe amount of peaking is determined to be correct. In that case, furtheradjustment to the amount of peaking may not be necessary. In suchmanner, the correct amount of peaking is determined for the particularset of temperature and voltage conditions. The parameters determined forthose conditions are then stored. The method may now continue foranother set of temperature and voltage conditions.

In the performance of the above method (FIG. 7) it is believed thattemperatures may be subjected to a wider changes than the voltage. Itmay also be difficult to tune the chip supply voltage duringcalibration. However, if one can vary the chip supply voltage by using avoltage regulator it is feasible to tune the bandwidth at differentsupply voltage levels. Temperature calibration alone may be sufficient.During the life of the chip, for each power supply voltage level, thechip has a capability of tuning the bandwidth of the transmitter atwhatever the supply voltage it sees. In this way, the on-chipcalibration system compensates for the aging process of the chip.

FIG. 9 shows a block diagram of an example design flow 900. Design flow900 may vary depending on the type of IC being designed. For example, adesign flow 900 for building an application specific IC (ASIC) maydiffer from a design flow 900 for designing a standard component. Designstructure 920 is preferably an input to a design process 910 and maycome from an IP provider, a core developer, or other design company ormay be generated by the operator of the design flow, or from othersources. Design structure 920 can include a transmitter 200 of amicroelectronic element (FIG. 2A) and other circuitry, e.g., 205, 210,220 (FIG. 2A) in the form of schematics or HDL, a hardware-descriptionlanguage (e.g., Verilog, VHDL, C, etc.). Design structure 920 may becontained on one or more machine readable medium. For example, designstructure 920 may be a text file or a graphical representation of thetransmitter 200. Design process 910 preferably synthesizes (ortranslates) CMOS latch into a netlist 980, where netlist 980 is, forexample, a list of wires, transistors, logic gates, control circuits,I/O, models, etc. that describes the connections to other elements andcircuits in an integrated circuit design and recorded on at least one ofmachine readable medium. This may be an iterative process in whichnetlist 980 is resynthesized one or more times depending on designspecifications and parameters for the circuit.

Design process 910 may include using a variety of inputs; for example,inputs from library elements 930 which may house a set of commonly usedelements, circuits, and devices, including models, layouts, and symbolicrepresentations, for a given manufacturing technology (e.g., differenttechnology nodes, 32 nm, 45 nm, 90 nm, etc.), design specifications 940,characterization data 950, verification data 960, design rules 970, andtest data files 985 (which may include test patterns and other testinginformation). Design process 910 may further include, for example,standard circuit design processes such as timing analysis, verification,design rule checking, place and route operations, etc. One of ordinaryskill in the art of integrated circuit design can appreciate the extentof possible electronic design automation tools and applications used indesign process 910 without deviating from the scope and spirit of theinvention. The design structure of the invention is not limited to anyspecific design flow.

Design process 910 preferably translates an embodiment of the inventionas shown in FIGS. 2 through 7, along with any additional integratedcircuit design or data (if applicable), into a second design structure990. Design structure 990 resides on a storage medium in a data formatused for the exchange of layout data of integrated circuits (e.g.information stored in a GDSII (GDS2), GL1, OASIS, or any other suitableformat for storing such design structures). Design structure 990 maycomprise information such as, for example, test data files, designcontent files, manufacturing data, layout parameters, wires, levels ofmetal, vias, shapes, data for routing through the manufacturing line,and any other data required by a semiconductor manufacturer to producean embodiment of the invention as shown in FIGS. 2 through 7. Designstructure 990 may then proceed to a stage 995 where, for example, designstructure 990: proceeds to tape-out, is released to manufacturing, isreleased to a mask house, is sent to another design house, is sent backto the customer, etc.

While the invention has been described in accordance with certainpreferred embodiments thereof, many modifications and enhancements canbe made thereto without departing from the true scope and spirit of theinvention, which is limited only by the claims appended below.

1. A design structure embodied in a machine-readable medium used in adesign process, the design structure comprising: a transmitter having afrequency response controllable in accordance with an operationalparameter; storage operable to store operational parameters forcontrolling a frequency response of the transmitter under each of aplurality of corresponding operating conditions; at least one sensoroperable to detect at least one operating condition; and a controlcircuit operable in response to a change in the detected operatingcondition to use the stored operational parameter corresponding to thedetected operating condition to control the frequency response of thetransmitter.
 2. The design structure as claimed in claim 1, wherein thedetected operating condition includes a temperature of themicroelectronic element and a power supply voltage level supplied to themicroelectronic element.
 3. The design structure as claimed in claim 1,wherein the transmitter includes an adjustable peaking element, whereinthe control circuit is operable to apply the stored operationalparameter to control a peaking function of the adjustable peakingelement.
 4. The design structure as claimed in claim 1, wherein thestorage is operable to store an operational parameter for each of aplurality of sets of operating conditions, each set of operatingconditions including values of at least two variables; and the values ofat least two variables include temperature and a power supply voltagelevel.
 5. The design structure as claimed in claim 4, wherein thecontrol circuit is operable to determine the operational parameters forthe plurality of sets of operating conditions when the transmitter ispowered on from an off state and wherein the transmitter is operable totransmit data serially over a cable external to the microelectronicelement and the values of the at least two variables includes at leastone of (a) a length of a cable to which the transmitter is coupled totransmit output or (b) a data transmission rate for transmitting data bythe transmitter.